The organic electronics community has benefited tremendously from the development of palladium-catalyzed cross-coupling reactions, which offer facile access to a wide range of chemical structures that would otherwise be challenging to achieve. This capability has enabled structure-property relationship studies that provide design parameters for useful organic materials. Improved processability of organic materials encourages these routes because replacement of inorganic semiconductors with organic surrogates has the potential to decrease device fabrication costs significantly. The Pd catalyzed direct arylation of halides or pseudo-halides or their derivatives has been rapidly developing to the point where only minute amounts of undesired side products are generated upon coupling. While the mechanistic details of the Pd insertion to the activated C—H bond are not fully understood, successful protocols have been developed for the coupling of thienyl-based molecules to a wide variety of organic halides.
Dehydrogenative cross-coupling is an attractive method to carry out the synthesis of thiophene-based conjugated polymers. This direct heteroarylation polymerization (DHAP) leads to more easily prepared conjugated polymers than those from standard Suzuki and Stille polymerizations. The absence of phosphine in the reaction mixture avoids any phosphine incorporation into the polymer backbone, which complicates polymer purification. The residual contaminants left in conjugated polymers are associated with poor performances of electronic devices therefrom. Impurities from catalysts, such as those comprising Sn, Pd, and Br, can act as charge trapping sites that hamper efficient charge transport processes. Therefore, minimization or avoidance of such impurities is critical for many applications of these polymers. To this end, the preparation of electrochromic polymers including donor-acceptor DA copolymers by the DHAP method is attractive.